1. Field of the Invention
The purpose of the invention is principally to provide a phased reflector array and an antenna including such an array.
With such an array, the phase of a wave, for example plane or cylindrical reflected on itself, may be locally modified. With such an array the electromagnetic energy beams of an electronic scan antenna may be focused and/or deflected.
2. Description of the Prior Art
Reflectors are already known, generally plane, and forms a mosaic or array of modules. Each module includes an elementary antenna and a phase shifter closed on a short circuit. A wave, whose beam it is desired to direct, is transmitted by an ultra-high frequency source in the direction of the array. The wave is picked up by the elementary antennae and undergoes a first phase shift on passing through the phase shifters, is reflected from the short circuits, passes again through the phase shifters and is radiated by the elementary antennae. By controlling, using electronic means, the phase shift provided by the phase shifters, the phase of the transmitted wave may be controlled at any point in the array. Such arrays are described by F. GAUTIER in "Reseau reflecteur" TH-CSF Revue March 1972, vol. 4, no. 1, pages 89-104 and by Oliver and Knittel in "Phased arrays antennae" Artech house, page 23.
Furthermore, it is known that the variation of the reactive impedance for example of a dipole placed in front of a metal reflector causes variation of the phase of the reflected wave.
Known arrays have the great drawback of requiring perfect or substantially perfect matching of the elementary antennae. In fact, on reception by the array any mismatching causes the partial reflection of a part of the incident energy instead of its transmission, the phase of the directly reflected energy is not controlled by the phase shifter. On emission by the array, any mismatching causes reflection towards the phase shifter of the energy which would normally be transmitted, this energy therefore undergoes twice the double passage through the phase shifter. At the time of transmission, the waves not having the desired phase shift, disturb the formation of the energy beam. Now, it has proved very difficult in practice to provide precise and uniform matching of all the elementary sources of the array.
In addition, it is not possible in practice to construct a phase shift module array capable of working in the millimetric bands. For these bands, the modules must have small dimensions, less than the wave length; the array must include a very large number of them.